Previously, many types of lifting systems have been used in endeavoring to provide an effective means to raise or lower a top on a van that has been converted or built by the original equipment manufacturer to function as a camper. This type of lifting operation has, in the past, been limited to hand cranks, spring loaded panels, opposed hinge struts lifted by hand or hydraulic systems added to the vehicle.
A search of the prior art did not disclose any patents that possess the novelty of the instant invention, however the following U.S. patents are considered related:
Patent Number Inventor Issue Date 3,981,529 Bontrager Sep. 21, 1976 4,201,413 Rowe May 6, 1980 4,362,258 French Dec. 7, 1982 4,630,627 Windows et al. Dec. 23, 1986 4,981,319 Gerzeny et al. Jan. 1, 1991
Bontrager in U.S. Pat. No. 3,981,529 teaches a camper that has a wheeled body and a top that is shiftable between collapsed and elevated positions, relative to the body. A crank mechanism is used to raise and lower the top. In one direction of rotation the crank is interlocked to prevent opposite rotation when the top is raised. Reverse rotation of the crank releases a ratchet to permit lowering the top.
U.S. Pat. No. 4,201,413 issued to Rowe teaches a folding apparatus for expandable top camper bodies including lifting and supporting apparatus. Each panel has a bi-fold panel consisting or two foldable panel sections hinged to each other and to the lateral wall of the camper the hinges are spring loaded to self actuate and push the top up to its expanded position and retain its placement. Resilient side stays having pre-formed crimps induce folding and guide the flexible fabric siding of the camper during folding to prevent wrinkling.
French in U.S. Pat. No. 4,362,258 discloses an add-on roof assembly for use in converting a van into a camper. The invention is adapted to be installed as a unit and includes a mounting base for fitting snugly over the rim of the van top. A pop-up top nests with the base when in a lowered position. The top is of two-ply construction providing ventilation between the plies.
Windows et al. in U.S. Pat. No. 4,630,627 teaches a collapsible frame structure that has a upper frame section connected to a base frame section using hinged struts. Both the upper frame and the base frame have a pair of rigid frame members pivotally connected by opposed rigid frame members. The hinge members fold inwardly and collapse outward to expand the section. A pair of winches mount to the base and connect to the struts extending the struts to raise the frame. Stabilizing members are mounted to an upper portion of the struts to balance the weight of the upper section enabling the struts to extend easily.
U.S. Pat. No. 4,981,319 issued to Gerzeny et al. is for a hydraulic lifting system for use in raising and lowering a top covering an opening in a vehicle roof The system includes a number of lifting linkages that are slideably attached to the support structure such that at least pair of linkages are attached to opposing support structure and also each lifting linkage is pivotally attached to the top. A number of hydraulic cylinders are mounted on the structure and interface with each pair of lifting linkages. Actuation of the hydraulic device urges the shafts to move in a push-pull relationship with the lifting linkages raising and lowering the top. It will be noted that hydraulic systems are subject to leakage and if one of the cylinders bypasses only a small amount of fluid the roof will not be raised in unison and could cause catastrophic results.